arch/x86/boot/compressed/pagetable.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This code is used on x86_64 to create page table identity mappings on
   4  * demand by building up a new set of page tables (or appending to the
   5  * existing ones), and then switching over to them when ready.
   6  *
   7  * Copyright (C) 2015-2016  Yinghai Lu
   8  * Copyright (C)      2016  Kees Cook
   9  */
  10
  11 /*
  12  * Since we're dealing with identity mappings, physical and virtual
  13  * addresses are the same, so override these defines which are ultimately
  14  * used by the headers in misc.h.
  15  */
  16 #define __pa(x)  ((unsigned long)(x))
  17 #define __va(x)  ((void *)((unsigned long)(x)))
  18
  19 /*
  20  * The pgtable.h and mm/ident_map.c includes make use of the SME related
  21  * information which is not used in the compressed image support. Un-define
  22  * the SME support to avoid any compile and link errors.
  23  */
  24 #undef CONFIG_AMD_MEM_ENCRYPT
  25
  26 #include "misc.h"
  27
  28 /* These actually do the work of building the kernel identity maps. */
  29 #include <asm/init.h>
  30 #include <asm/pgtable.h>
  31 /* Use the static base for this part of the boot process */
  32 #undef __PAGE_OFFSET
  33 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
  34 #include "../../mm/ident_map.c"
  35
  36 /* Used by pgtable.h asm code to force instruction serialization. */
  37 unsigned long __force_order;
  38
  39 /* Used to track our page table allocation area. */
  40 struct alloc_pgt_data {
  41         unsigned char *pgt_buf;
  42         unsigned long pgt_buf_size;
  43         unsigned long pgt_buf_offset;
  44 };
  45
  46 /*
  47  * Allocates space for a page table entry, using struct alloc_pgt_data
  48  * above. Besides the local callers, this is used as the allocation
  49  * callback in mapping_info below.
  50  */
  51 static void *alloc_pgt_page(void *context)
  52 {
  53         struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
  54         unsigned char *entry;
  55
  56         /* Validate there is space available for a new page. */
  57         if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
  58                 debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
  59                 debug_putaddr(pages->pgt_buf_offset);
  60                 debug_putaddr(pages->pgt_buf_size);
  61                 return NULL;
  62         }
  63
  64         entry = pages->pgt_buf + pages->pgt_buf_offset;
  65         pages->pgt_buf_offset += PAGE_SIZE;
  66
  67         return entry;
  68 }
  69
  70 /* Used to track our allocated page tables. */
  71 static struct alloc_pgt_data pgt_data;
  72
  73 /* The top level page table entry pointer. */
  74 static unsigned long top_level_pgt;
  75
  76 /*
  77  * Mapping information structure passed to kernel_ident_mapping_init().
  78  * Due to relocation, pointers must be assigned at run time not build time.
  79  */
  80 static struct x86_mapping_info mapping_info = {
  81         .page_flag       = __PAGE_KERNEL_LARGE_EXEC,
  82 };
  83
  84 /* Locates and clears a region for a new top level page table. */
  85 void initialize_identity_maps(void)
  86 {
  87         /* Init mapping_info with run-time function/buffer pointers. */
  88         mapping_info.alloc_pgt_page = alloc_pgt_page;
  89         mapping_info.context = &pgt_data;
  90
  91         /*
  92          * It should be impossible for this not to already be true,
  93          * but since calling this a second time would rewind the other
  94          * counters, let's just make sure this is reset too.
  95          */
  96         pgt_data.pgt_buf_offset = 0;
  97
  98         /*
  99          * If we came here via startup_32(), cr3 will be _pgtable already
 100          * and we must append to the existing area instead of entirely
 101          * overwriting it.
 102          *
 103          * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
 104          * the top-level page table is allocated separately.
 105          *
 106          * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
 107          * cases. On 4-level paging it's equal to 'top_level_pgt'.
 108          */
 109         top_level_pgt = read_cr3_pa();
 110         if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
 111                 debug_putstr("booted via startup_32()\n");
 112                 pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
 113                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
 114                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 115         } else {
 116                 debug_putstr("booted via startup_64()\n");
 117                 pgt_data.pgt_buf = _pgtable;
 118                 pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
 119                 memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
 120                 top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
 121         }
 122 }
 123
 124 /*
 125  * Adds the specified range to what will become the new identity mappings.
 126  * Once all ranges have been added, the new mapping is activated by calling
 127  * finalize_identity_maps() below.
 128  */
 129 void add_identity_map(unsigned long start, unsigned long size)
 130 {
 131         unsigned long end = start + size;
 132
 133         /* Align boundary to 2M. */
 134         start = round_down(start, PMD_SIZE);
 135         end = round_up(end, PMD_SIZE);
 136         if (start >= end)
 137                 return;
 138
 139         /* Build the mapping. */
 140         kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
 141                                   start, end);
 142 }
 143
 144 /*
 145  * This switches the page tables to the new level4 that has been built
 146  * via calls to add_identity_map() above. If booted via startup_32(),
 147  * this is effectively a no-op.
 148  */
 149 void finalize_identity_maps(void)
 150 {
 151         write_cr3(top_level_pgt);
 152 }